Cap piece for pivot bearings



March 10, 1959 SElTz 2,876,618

CAP PIECE FOR PIVOT BEARINGS Filed Aug. 23, 1955 h m 3 .STAAKUL.

United States Patent CAP PIECE FOR PIVOT BEARINGS Pierre Seitz, Les Brenets, Switzerland Application August 23, 1955, Serial No. 530,138

Claims priority, application Switzerland October 9, 1954 8 Claims. (Cl. 58-140) This invention relates to cap pieces for pivot bearings, such as bearings for measuring apparatus, timepieces and the like.

The cap pieces used in most of the cases comprise a cap jewel forced in a metal setting, and the inner surface of these jewels-i. e. the surface against which the pivot axially butts--in a plane surface.

In the bearings provided with such a cap piece, the oil drop which should lubricate the pivot as well as the walls of the bore of the pierced jewel very often spreads on the plane surface of the cap jewel until it comes in contact with the setting carrying this cap jewel.

Since oil has more affinity for metal than for the corundum of the jewel, it consequently flows towards the setting and entirely disappears from the places of the bearing which it should lubricate.

Several attempts have already been made in order to avoid this drawback. For this purpose, grooves concentric to the jewel have been provided either in the latter or in its setting to avoid spreading of the oil. It has, however, been observed in there constructions that said grooves are soon full of oil. If these grooves are pro- 2,876,618 Patented Mar. 10, 1959 2 ranging said projection so that its top face remains behind the inner face of the cap piece.

Further objects of the invention will appear in the course of the following description.

Two embodiments of a cap piece according to the invention are represented diagrammatically and by way of example in the drawings annexed to this specification and forming a part thereof.

In the drawings:

Figs. 1 and 2 are diametrical cross-sections showing each one of said embodiments.

By referring to Fig. 1, a cap jewel 1 made of synthetic corundum, is provided with a circular countersink 3 in its inner face 2 which is turned towards the pierced elements of the bearing (not shown). A projection 4, also circular, extends from the center of countersink 3. Projection 4 comprises a top face 5, plane, circular and extending in parallel to the inner face 2 of the jewel 1. The projection 4 comprises also a wall 6 which is cylindrical at least in the vicinity of the top face 5 with which it defines a right angle thus constituting a very strong bar for the oil drop 7 situated on face 5.

This cap piece is particularly suitable for hearings in which the cap jewel is freely located on a pierced jewel. The cap jewel will indeed bear by means of its circular edge 8 on the rounded top surface of the pierced jewel,

while avoiding any contact between face 5 of projection 4 and the pierced jewel, because face 5 is located beyond the inner face 2 of jewel 1. This particular arrangement of surfaces 2 and 5 has still another advantage. If the oil drop placed on face 5 does not extend beyond face 2 of the jewel, the latter can be oiled and then handled vided in the jewel itself as till now, in a single operation,

the working means known do not allow cutting sharp edges in one operation so that the oil merely flows along the rounded surface portions which constitute the edge of said grooves and soon fill the later. On the contrary, if the grooves are provided in the setting, even a sharp edge does not constitute a bar for the oil because of its afiinity for the metal.

It is therefore an object of the invention to provide a cap piece for a pivot bearing on which the oil remains at the places which it must lubricate. For this purpose the inner surface of the cap piece according to the invention is countersunk anda small portion projects from the bottom of this countersink, said portion having a top face which is plane, circular and parallel to the jewel inner face. The lateral face of this projection is cylindrical at least in the vicinity of said top face.

It has been observed that oil perfectly adheres on a plane surface delimited by a cylindrical wall of a certain height. An oil drop put on such a surface is so well in equilibrium that even if the cap piece is subjected to an impact, the oil drop always remains on said surface.

The cap piece can either be made in one piece of the same material, such as corundum, provided that the cylindrical wall of said projection extends over a height of about 0.0012 from said top surface, or in two pieces the first of which thereby being countersunk and presenting a circular opening in which a second cylindrical piece is set with force fit, said second piece forming said projection. In the latter case the second one of said pieces preferably projects out of the first one over at least 0.0024".

It is also an object of the invention to provide a circular countersink in the inner face of the cap piece and to locate said projection in the center of said countersink.

Still a further object of the invention consists in arwithout any particular care because the oil drop cannot come in contact with any support, such as the surface of the bench, even if the jewel lies on this surface with its inner face down.

The cap piece represented in Fig. 2 is made of two pieces. It comprises a first piecel', made, for instance, of brass, the form of which corresponds to that of a usual cap jewel. This piece 1' is provided with a countersink 3' in its inner face 2. as well as with a circular opening 9 in the center of countersink 3'. A second piece constituted by a cylindrical block 10 of hard material, for instance, corundum, is set with force fit into opening 9 so that the top face 5' of block 10 extends-above the bottom of countersink 3. The sizes of piece 1 and those of block 10 can be chosen so that face 5 of block 10 is situated on the same level as surface 2 of piece 1 while the other plane face of block 10 is fiush with the outer face of piece 1.

Tests made with cap pieces according to both en1bodiments described above have shown that the oil drop which is placed on the top face 5 or 5 of the central projection of these cap pieces, was in so stable an equilibrium that if disassembling an oiled bearing, the oil of this hearing which lubricated the pierced jewel gathers itself on the top face of the central projection of the cap piece.

It must be noted that the stability observed is due first to the fact that said top face is plane and second to the fact that said face is delimited by a cylindrical wall defining a right angle with it. It has indeed been observed with a top face which was only very slightly concave, that even the smallest oil quantity which would extend beyond the edges of the said concave face, flows immediately along the cylindrical wall of the central projection. On the contrary, with a plane face (5, 5') the cylindrical wall needs only to extend over at least 0.0012" in a cap piece according to the first embodiment, and over at least 0.0024" in a cap piece according to the second embodiment.

While two examplesof the invention have been described in detail, it will be understood that many changes in the form, sizes and arrangement of parts may be resorted to without departing from the-spirit of the advantages of the invention which is only limited by the subjoined claims.

I claim:

1. A cap piece for a pivot bearing of an apparatus,

a watch and the like, comprising an inner face, a countersink insaid inner face, a projection constituted by a separate piece set with force fit in an opening formed in said cap piece, said projection protruding from the bottom of said countersink and having an end face which is circular, plane and parallel to said inner face, and a side face which is cylindrical at least in the vicinity of said end face.

2. A cap piece according to claim 1, in which said projection extends at least over 0.0024 from the bottom of said countersink.

3. A lubricating arrangement for a pivot bearing comprising, in combination, a cap member including'a peripheral portion for engaging pierced jewel means, a central portion having a circular planar lubricating face adapted to support an oil drop thereon, and a cylindrical face extending inwardly from and normal to said circular planar face for holding said oil drop on said circular planar face by surface tension; and an annular connecting portion having an annular face surrounding and merging into said cylindrical face whereby a balance staff pivot associated with said pierced jewel and located opposite said planar face is lubricated by said oil drop.

4. A lubricating arrangement for a pivot bearing comprising, in combination, a cap member including a peripheral portion for engaging pierced jewel means, a central portion having a circular planar lubricating face adapted to support an oil drop thereon, and a cylindrical face extending inwardly from and normal to said circular planar face for holding said oil drop on said circular planar face by surface tension, said cylindrical face extending inwardly from said lubricating face for a distance of approximately .0012 inches; and an annular connecting portion having an annular face surrounding and merging into said cylindrical face whereby a balance staff pivot associated with said pierced jewel and located opposite said planar face is lubricated by said oil drop.

5. A lubricating arrangement for a pivot bearing comprising, in combination, a cap member including a peripheral portion for engaging pierced jewel means at points located in a first plane, a central portion having a circular planar lubricating face adapted to support an oil drop thereon and located in a second plane parallel to and spaced inwardly from said first plane, and a cylindrical face extending inwardly from and normal to said circular planar lubricating face for holding said oil drop on said circular planar lubricating face by surface tension; and an annular connecting portion having an annular face surrounding and merging into said cylindrical face whereby a balance staff pivot associated with said pierced jewel and located opposite said planar lubricating face is lubricated by said oil drop.

6. A lubricating arrangement for a pivot bearing comprising, in combination, a cap member including a peripheral portion for engaging pierced jewel means at points located in a first plane, a central portion having a circular planar lubricating face adapted to support an oil drop thereon and located in a second plane parallel to and spaced inwardly from said first plane, and a cylindrical face extending inwardly from and normal to said circular planar lubricating face for holding said oil drop on said circular planar lubricating face by surface tension, said cylindrical face extending inwardly from said lubricating face for a distance of approximately .0012 inch; and an annular connecting portion having an annular face surrounding and merging into said cylindrical face whereby a balance staff pivot associated with said pierced jewel and located opposite said planar lubricating face is lubricated by said oil drop.

7. A lubricating arrangement for a pivot bearing comprising, in combination, a cap member including a peripheral portion having an outer annular face located in a'first plane for engaging pierced jewel means at points located in said first plane, a central portion having a circular planar lubricating face adapted to support an oil drop thereon and located in a second plane parallel to and spaced inwardly from said first plane, and a first cylindrical face extending inwardly from said lubricating face, said first cylindrical face including an outermost portion adjacent and normal to said lubricating face and forming therewith a sharp edgefor holding said oil drop on said lubricating face by surface tension; and an annular connecting portion having a second cylindrical face extending inwardly from said outer annular face, and an inner annular face surrounding and merging into said first cylindrical face whereby a balance staff pivot associated with said pierced jewel and located opposite said planar face is lubricated by said oil drop.

8. A lubricating arrangement for a pivot bearing comprising, in combination, a cap member including a peripheral portion for engaging pierced jewel means and a recessed inner portion formed with an opening therethrough; and a lubricating member passing through said opening and having a circular planar face spaced outwardly from said recessed portion and being adapted to support an oil drop thereon, and a cylindrical face extending inwardly from and normal to said circular planar face for holding said oil drop on said circular planar face by surface tension whereby a balance staff pivot associated with said pierced jewel and located opposite said planar face is lubricated by said oil drop.

References Citedin the file of .this patent UNITED STATES PATENTS 2,330,729 Meredith et al. Sept. 28, 1943 FOREIGN PATENTS 843,680 Germany July 10, 1952 156,949 Switzerland Nov. 1, 1932 287,938 Switzerland Apr. 6, 1953 310,555 Switzerland Dec. 16, 1955 

